Ultrastrong spinodoid alloys enabled by electrochemical dealloying and refilling.

We present an extreme case of composition-modulated nanomaterial formed by selective etching (dealloying) and electrochemical refilling. The product is a coarse-grain polycrystal consisting of two interwoven nanophases, with identical crystal structures and a cube-on-cube relationship, separated by smoothly curved semicoherent interfaces with high-density misfit dislocations. This material resembles spinodal alloys structurally, but its synthesis and composition modulation are spinodal-independent. Our Cu/Au "spinodoid" alloy demonstrates superior mechanical properties such as near-theoretical strength and single-phase-like behavior, owing to its fine composition modulation, large-scale coherence of crystal lattice, and smoothly shaped three-dimensional (3D) interface morphology. As a unique extension of spinodal alloy, the spinodoid alloy reported here reveals a number of possibilities to modulate the material's structure and composition down to the nanoscale, such that further improved properties unmatchable by conventional materials can be achieved.

Surface Triple Junctions Govern the Strength of a Nanoscale Solid.

Surface triple junctions (STJs), i.e., the termination lines of grain boundaries at solid surface, are the common line defects in polycrystalline materials. Compared with planar defects such as grain boundaries and surfaces, STJ lines are usually overlooked in a material's strengthening although abundant atoms may reside at STJs in many nanomaterials. In this study, by in situ compression of coarse-grained and nanocrystalline nanoporous gold samples in an electrochemical environment, the effect of STJs on the strength of nanoporous gold was successfully decoupled from grain-boundary and surface effects. We found that the strength of nanoporous gold became sensitive to STJ modification when ligament size was decreased to below ∼100 nm, indicating that STJs started to influence ligament strength at sub-100 nm scale. This STJ effect was associated with the emission of dislocations from STJs during plastic deformation. Our findings strongly suggest that the structure and chemistry at STJs should be considered in understanding the mechanical response of sub-100 nm scale materials.

Transition from Homogeneous to Localized Deformation in Nanoporous Gold.

We report a transition from homogeneous deformation to localized densification for nanoporous gold (NPG) under compression, with its solid fraction (φ) increasing to above ∼1/3. Results obtained herein suggest that this transition is inverted compared to that of conventional porous materials. Consequently, under compression, the low-density NPGs with φ<1/3 showed evident strain hardening, whereas a stress plateau was observed for high-density NPGs with φ>1/3, which is contrary to the established notions for conventional porous materials. The ligament pinch-offs and bending-dominated structures are responsible for the homogeneous deformation of low-density NPGs. For high-density NPGs, the compression- or tension-dominated structure enables the collective strain bursts in nanoligaments, resulting in localized densification and stress plateau in their compression curves. In addition to the nanosize effect, the surface-diffusion-mediated topology evolution and the large-scale crystal-lattice coherency arising from the large grain size are also decisive to the mechanical response of dealloyed NPGs, which might be universal for self-organized nanonetwork materials.

Sealing-free fast-response paraffin/nanoporous gold hybrid actuator.

Paraffin-based actuators can deliver large actuation strokes and high actuation stress, but often suffer from a low response rate and leaking problems. Here, we report a new paraffin/metal hybrid actuator, which was fabricated by infiltrating nanoporous gold with paraffin. It exhibits a fast actuation rate owing to the high thermal conductivity of the inter-connected metal phase, and requires no external sealing because liquid paraffin can be well confined in nanoscale channels, due to the large capillarity. We found that in this hybrid actuator, the stress generated by actuation is negligibly small when the characteristic size of the nanoporous gold (L) is above ∼70 nm, and increases dramatically with a decreasing size when L < âˆ¼70 nm. The large actuation stress in samples with L < âˆ¼70 nm is ascribed to a 'smaller is stronger' effect in paraffin wax-the paraffin in smaller pores can sustain larger tensile stress, and thus the contraction of paraffin during cooling can be translated into larger compression stress and strain energy in a metal framework, leading to a larger actuation stress and energy. We also demonstrate that complex actuation motions can be achieved by incorporating hierarchical-structured nanoporous metal with paraffin.

Anomalous low strain induced by surface charge in nanoporous gold with low relative density.

The surface stress induced axial strain in a fiber-like solid is larger than its radical strain, and is also greater than the radical strain in similar-sized spherical solids. It is thus envisaged that the surface-induced macroscopic dimension change (i.e., actuation strain) in nanoporous gold (NPG) increases with decreasing relative density, or alternatively, with an increasing ratio between volumes of fiber-like ligaments and sphere-like nodes. In this study, electrochemical actuations of NPG with similar structure sizes, same (oxide-covered) surface state but different relative densities were characterized in situ in response to surface charging/discharging. We found that the actuation strain amplitude did not increase, but decreased dramatically with decreasing relative density of NPG, in contrast to the above prediction. The actuation strain decreased abruptly when the relative density of NPG was decreased to below 0.25, when the Au content in the AuAg precursor was below 20 at%. Further studies indicate that this anomalous behavior cannot be explained by potential- or size-dependences of the elasticity, the structure difference arising from different dealloying rates, or additional strain induced by the external load during dilatometry experiments. In NPG with low relative density, mutual movements of nano-ligaments may occur in the pore space and disconnected regions, which may compensate the local strain in ligaments and account for the anomalous low actuation strain in macroscopic NPG samples.

Responsive nanoporous metals: recoverable modulations on strength and shape by watering.

Many biological materials can readily modulate their mechanical properties and shape by interacting with water in the surrounding environment, which is essential to their high performance in application. In contrast, typical inorganic materials (such as the metals) cannot change their strength and shape without involving thermal/mechanical treatments. By introducing nano-scale porous structure and exploiting a simple physical concept-the water-capillarity in nanopores, here we report that a 'dead' metal can be transformed into a 'smart' material with water-responsive properties. We demonstrate that the apparent strength, volume and shape of nanoporous Au and Au(Pt) can be modulated in situ, dramatically and recoverably, in response to water-dipping and partial-drying. The amplitude of strength-modulation reaches 20 MPa, which is nearly 50% of the yield strength at initial state. This approach also leads to reversible length change up to 1.3% in nanoporous Au and a large reversible bending motion of a bi-layer strip with tip displacement of ∼20 mm, which may be used for actuation. This method is simple and effective, occurring in situ under ambient conditions and requiring no external power, analogous to biological materials. The findings may open up novel applications in many areas such as micro-robotics and bio-medical devices.

Nanoporous Au-Pt alloys as large strain electrochemical actuators.

Nanoporous Au-Pt alloys with pore- and ligament size down to few nanometers were fabricated by dealloying Ag-Au-Pt. Owing to the small structure size and large specific surface area, the surface stress and its variation give rise to significant stress and strain in the bulk of these materials. In fact, dilatometry experiments find electrochemical actuation with large reversible strain amplitude. The linear strain reaches approximately 1.3% and strain energy density is up to 6.0 MJ/m(3). The associated stresses may approach the elastic limit of the alloy.

Effect and satisfaction of outpatient services by precision valuation reservation registration.

BACKGROUND: Due to improvements in living standards, people are now paying more attention to their health. In China, more patients choose to go to large or well-known hospitals, which leads to constant crowding of outpatient clinics in these hospitals. AIM: To establish precision valuation reservation registration aimed at shortening waiting time, improving patient experience and promoting the satisfaction of outpatients and medical staff. METHODS: On the basis of the implementation of a conventional appointment system, more reasonable time intervals were set for different doctors by evaluating the actual capacity of each doctor to receive patients, and appointment times were made more accurate through intervention. The change in consultation waiting time of patients was then compared. Correlations between the consultation waiting time of patients and the satisfaction of patients or satisfaction of medical staff were analyzed. RESULTS: After precision valuation reservation registration, the average consultation waiting time of patients reduced from 18.47 min to 10.11 min (t = 8.90, P < 0.001). The satisfaction score of patients increased from 91.33 to 96.27 (t = -8.62, P < 0.001), and the satisfaction score of medical staff increased from 90.51 to 96.04 (t = -10.50, P < 0.001). The consultation waiting time of patients was negatively correlated with their satisfaction scores (γ = -0.89, P < 0.001). The consultation waiting time of patients was also negatively correlated with medical staff satisfaction scores (γ = -0.96, P < 0.001). CONCLUSION: Precision valuation reservation registration significantly shortened outpatient waiting times and improve the satisfaction of not only patients but also medical staff. This approach played an important role in improving outpatient services, provided a model that is supported by relevant evidence and could continuously improve the quality of management. Precision valuation reservation registration is worth promoting and applying in the clinic.

Light, strong, and stable nanoporous aluminum with native oxide shell.

Aluminum (Al) metal is highly reactive but has excellent corrosion resistance because of the formation of a self-healing passive oxide layer on the surface. Here, we report that this native aluminum oxide shell can also stabilize and strengthen porous Al when the ligament (strut) size is decreased to the submicron or nanometer scale. The nanoporous Al with native oxide shell, which is a nanoporous Al-Al2O3 core-shell composite self-organized in a galvanic replacement reaction, is nonflammable under ambient conditions and stable against coarsening near melting temperatures. This material is stronger than conventional foams of similar density consisting of pure Al or Al-based composites, and also lighter and stronger than most nanoporous metals reported previously. Its light weight, high strength, and excellent stability warrant the explorations of functional and structural applications of this material, if more efficient and scalable synthesis processes are developed in the future.

Galvanic Replacement Reaction as a Route to Prepare Nanoporous Aluminum for UV Plasmonics.

There is a growing interest in extending plasmonics applications into the ultraviolet region of the electromagnetic spectrum. Noble metals are commonly used in plasmonic, but their intrinsic optical properties limit their use above 350 nm. Aluminum is probably the most suitable material for UV plasmonics, and in this work we fabricated substrates of nanoporous aluminum starting from an alloy of Al2Mg3. The porous metal is obtained by means of a galvanic replacement reaction. Such nanoporous metal can be exploited to achieve a plasmonic material suitable for enhanced UV Raman spectroscopy and fluorescence. Thanks to the large surface to volume ratio, this material represents a powerful platform for promoting interaction between plasmonic substrates and molecules in the UV.

A material with electrically tunable strength and flow stress.

The selection of a structural material requires a compromise between strength and ductility. The material properties will then be set by the choice of alloy composition and microstructure during synthesis and processing, although the requirements may change during service life. Materials design strategies that allow for a recoverable tuning of the mechanical properties would thus be desirable, either in response to external control signals or in the form of a spontaneous adaptation, for instance in self-healing. We have designed a material that has a hybrid nanostructure consisting of a strong metal backbone that is interpenetrated by an electrolyte as the second component. By polarizing the internal interface via an applied electric potential, we accomplish fast and repeatable tuning of yield strength, flow stress, and ductility. The concept allows the user to select, for instance, a soft and ductile state for processing and a high-strength state for service as a structural material.